1. Field of the Invention
The present invention relates to a zoom optical system and an image pickup apparatus provide with the same.
2. Description of the Related Art
In recent years, instead of silver-halide film cameras, digital cameras provided with solid-state image sensors, such as CCDs (charge coupled devices) and CMOSs (complementary metal-oxide semiconductors), have constituted the main current. Such digital cameras are available in various types ranging from a high-function type for business use to a popular compact type. Of these, the popular compact type of digital camera has come to require a slim design, in addition to a compact design, so that the camera can be easily put into the pocket of clothing or bag and is handy to carry, in order to meet the need of a user who wants to readily enjoy photography. It is important that such small sized digital cameras are required to be hard and anti-dusty, because they are used and kept at any place.
Consequently, for a zoom optical system used in such digital cameras, a compacter design is required, and substantial quality and high dust-proof characteristic are required. A zoom optical system satisfying such requirements is shown in Japanese Patent No. 3493406 and Japanese patent Kokai No. 2007-156417.
The zoom optical system shown in Japanese patent No. 349406 comprises a first lens unit with negative power, a second lens unit with positive power, a third lend unit with positive power and a fourth lens unit with positive power. And, each lens unit is made of one plastic lens, respectively, the first and fourth lens units are stationary, and the variation of magnification is taken place by moving the second and third lens units on the optical axis.
Further, the zoom optical system shown in Japanese patent Kokai No. 2007-156417 comprises a first lens unit with negative power, a second lens unit with positive power, a third lens unit with positive power, and a fourth lens unite with positive power. And, the third lens unit comprises an aperture stop, a lens with positive power and a lens with negative power, the first and fourth lens units are stationary, and the second and third lens units are adapted to be moved upon zooming.